[PATCH 1/4] Support named cgroups hierarchies

From: Paul Menage
Date: Wed Jul 22 2009 - 15:51:37 EST

Support named cgroups hierarchies

To simplify referring to cgroup hierarchies in mount statements, and
to allow disambiguation in the presence of empty hierarchies and
multiply-bindable subsystems this patch adds support for naming a new
cgroup hierarchy via the "name=" mount option

A pre-existing hierarchy may be specified by either name or by
subsystems; a hierarchy's name cannot be changed by a remount
operation.

Example usage:

# To create a hierarchy called "foo" containing the "cpu" subsystem
mount -t cgroup -oname=foo,cpu cgroup /mnt/cgroup1

# To mount the "foo" hierarchy on a second location
mount -t cgroup -oname=foo cgroup /mnt/cgroup2


Signed-off-by: Paul Menage <menage@xxxxxxxxxx>

---

Documentation/cgroups/cgroups.txt | 19 ++++
kernel/cgroup.c | 186 +++++++++++++++++++++++++++----------
2 files changed, 157 insertions(+), 48 deletions(-)

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 6eb1a97..1f7cf9f 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -408,6 +408,25 @@ You can attach the current shell task by echoing 0:

# echo 0 > tasks

+2.3 Mounting hierarchies by name
+--------------------------------
+
+Passing the name=<x> option when mounting a cgroups hierarchy
+associates the given name with the hierarchy. This can be used when
+mounting a pre-existing hierarchy, in order to refer to it by name
+rather than by its set of active subsystems.
+
+The name should match [\w.-]+
+
+When passing a name=<x> option for a new hierarchy, you need to
+specify subsystems manually; the legacy behaviour of mounting all
+subsystems when none are explicitly specified is not supported when
+you give a subsystem a name.
+
+The name of the subsystem appears as part of the hierarchy description
+in /proc/mounts and /proc/<pid>/cgroups.
+
+
3. Kernel API
=============

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 18acba7..abca7e5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -23,6 +23,7 @@
*/

#include <linux/cgroup.h>
+#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/kernel.h>
@@ -60,6 +61,8 @@ static struct cgroup_subsys *subsys[] = {
#include <linux/cgroup_subsys.h>
};

+#define MAX_CGROUP_ROOT_NAMELEN 64
+
/*
* A cgroupfs_root represents the root of a cgroup hierarchy,
* and may be associated with a superblock to form an active
@@ -94,6 +97,9 @@ struct cgroupfs_root {

/* The path to use for release notifications. */
char release_agent_path[PATH_MAX];
+
+ /* The name for this hierarchy - may be empty */
+ char name[MAX_CGROUP_ROOT_NAMELEN];
};

/*
@@ -829,6 +835,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
seq_puts(seq, ",noprefix");
if (strlen(root->release_agent_path))
seq_printf(seq, ",release_agent=%s", root->release_agent_path);
+ if (strlen(root->name))
+ seq_printf(seq, ",name=%s", root->name);
mutex_unlock(&cgroup_mutex);
return 0;
}
@@ -837,6 +845,9 @@ struct cgroup_sb_opts {
unsigned long subsys_bits;
unsigned long flags;
char *release_agent;
+ char *name;
+
+ struct cgroupfs_root *new_root;
};

/* Convert a hierarchy specifier into a bitmask of subsystems and
@@ -851,9 +862,7 @@ static int parse_cgroupfs_options(char *data,
mask = ~(1UL << cpuset_subsys_id);
#endif

- opts->subsys_bits = 0;
- opts->flags = 0;
- opts->release_agent = NULL;
+ memset(opts, 0, sizeof(*opts));

while ((token = strsep(&o, ",")) != NULL) {
if (!*token)
@@ -873,11 +882,33 @@ static int parse_cgroupfs_options(char *data,
/* Specifying two release agents is forbidden */
if (opts->release_agent)
return -EINVAL;
- opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
+ opts->release_agent =
+ kstrndup(token + 14, PATH_MAX, GFP_KERNEL);
if (!opts->release_agent)
return -ENOMEM;
- strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
- opts->release_agent[PATH_MAX - 1] = 0;
+ } else if (!strncmp(token, "name=", 5)) {
+ int i;
+ const char *name = token + 5;
+ /* Can't specify an empty name */
+ if (!strlen(name))
+ return -EINVAL;
+ /* Must match [\w.-]+ */
+ for (i = 0; i < strlen(name); i++) {
+ char c = name[i];
+ if (isalnum(c))
+ continue;
+ if ((c == '.') || (c == '-') || (c == '_'))
+ continue;
+ return -EINVAL;
+ }
+ /* Specifying two names is forbidden */
+ if (opts->name)
+ return -EINVAL;
+ opts->name = kstrndup(name,
+ MAX_CGROUP_ROOT_NAMELEN,
+ GFP_KERNEL);
+ if (!opts->name)
+ return -ENOMEM;
} else {
struct cgroup_subsys *ss;
int i;
@@ -904,7 +935,7 @@ static int parse_cgroupfs_options(char *data,
return -EINVAL;

/* We can't have an empty hierarchy */
- if (!opts->subsys_bits)
+ if (!opts->subsys_bits && !opts->name)
return -EINVAL;

return 0;
@@ -932,6 +963,12 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
goto out_unlock;
}

+ /* Don't allow name to change at remount */
+ if (opts.name && strcmp(opts.name, root->name)) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
ret = rebind_subsystems(root, opts.subsys_bits);
if (ret)
goto out_unlock;
@@ -943,6 +980,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
strcpy(root->release_agent_path, opts.release_agent);
out_unlock:
kfree(opts.release_agent);
+ kfree(opts.name);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
unlock_kernel();
@@ -965,6 +1003,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
INIT_LIST_HEAD(&cgrp->pids_list);
init_rwsem(&cgrp->pids_mutex);
}
+
static void init_cgroup_root(struct cgroupfs_root *root)
{
struct cgroup *cgrp = &root->top_cgroup;
@@ -978,31 +1017,59 @@ static void init_cgroup_root(struct cgroupfs_root *root)

static int cgroup_test_super(struct super_block *sb, void *data)
{
- struct cgroupfs_root *new = data;
+ struct cgroup_sb_opts *opts = data;
struct cgroupfs_root *root = sb->s_fs_info;

- /* First check subsystems */
- if (new->subsys_bits != root->subsys_bits)
- return 0;
+ /* If we asked for a name then it must match */
+ if (opts->name && strcmp(opts->name, root->name))
+ return 0;

- /* Next check flags */
- if (new->flags != root->flags)
+ /* If we asked for subsystems then they must match */
+ if (opts->subsys_bits && (opts->subsys_bits != root->subsys_bits))
return 0;

return 1;
}

+static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
+{
+ struct cgroupfs_root *root;
+
+ /* Empty hierarchies aren't supported */
+ if (!opts->subsys_bits)
+ return NULL;
+
+ root = kzalloc(sizeof(*root), GFP_KERNEL);
+ if (!root)
+ return ERR_PTR(-ENOMEM);
+
+ init_cgroup_root(root);
+ root->subsys_bits = opts->subsys_bits;
+ root->flags = opts->flags;
+ if (opts->release_agent)
+ strcpy(root->release_agent_path, opts->release_agent);
+ if (opts->name)
+ strcpy(root->name, opts->name);
+ return root;
+}
+
static int cgroup_set_super(struct super_block *sb, void *data)
{
int ret;
- struct cgroupfs_root *root = data;
+ struct cgroup_sb_opts *opts = data;
+
+ /* If we don't have a new root, we can't set up a new sb */
+ if (!opts->new_root)
+ return -EINVAL;
+
+ BUG_ON(!opts->subsys_bits);

ret = set_anon_super(sb, NULL);
if (ret)
return ret;

- sb->s_fs_info = root;
- root->sb = sb;
+ sb->s_fs_info = opts->new_root;
+ opts->new_root->sb = sb;

sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
@@ -1039,48 +1106,44 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
void *data, struct vfsmount *mnt)
{
struct cgroup_sb_opts opts;
+ struct cgroupfs_root *root;
int ret = 0;
struct super_block *sb;
- struct cgroupfs_root *root;
- struct list_head tmp_cg_links;

/* First find the desired set of subsystems */
ret = parse_cgroupfs_options(data, &opts);
- if (ret) {
- kfree(opts.release_agent);
- return ret;
- }
-
- root = kzalloc(sizeof(*root), GFP_KERNEL);
- if (!root) {
- kfree(opts.release_agent);
- return -ENOMEM;
- }
+ if (ret)
+ goto out_err;

- init_cgroup_root(root);
- root->subsys_bits = opts.subsys_bits;
- root->flags = opts.flags;
- if (opts.release_agent) {
- strcpy(root->release_agent_path, opts.release_agent);
- kfree(opts.release_agent);
+ /*
+ * Allocate a new cgroup root. We may not need it if we're
+ * reusing an existing hierarchy.
+ */
+ {
+ struct cgroupfs_root *new_root = cgroup_root_from_opts(&opts);
+ if (IS_ERR(new_root)) {
+ ret = PTR_ERR(new_root);
+ goto out_err;
+ }
+ opts.new_root = new_root;
}

- sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
-
+ /* Locate an existing or new sb for this hierarchy */
+ sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
if (IS_ERR(sb)) {
- kfree(root);
- return PTR_ERR(sb);
+ ret = PTR_ERR(sb);
+ kfree(opts.new_root);
+ goto out_err;
}

- if (sb->s_fs_info != root) {
- /* Reusing an existing superblock */
- BUG_ON(sb->s_root == NULL);
- kfree(root);
- root = NULL;
- } else {
- /* New superblock */
+ root = sb->s_fs_info;
+ BUG_ON(!root);
+ if (root == opts.new_root) {
+ /* We used the new root structure, so this is a new hierarchy */
+ struct list_head tmp_cg_links;
struct cgroup *root_cgrp = &root->top_cgroup;
struct inode *inode;
+ struct cgroupfs_root *existing_root;
int i;

BUG_ON(sb->s_root != NULL);
@@ -1093,6 +1156,18 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
mutex_lock(&inode->i_mutex);
mutex_lock(&cgroup_mutex);

+ if (strlen(root->name)) {
+ /* Check for name clashes with existing mounts */
+ for_each_active_root(existing_root) {
+ if (!strcmp(existing_root->name, root->name)) {
+ ret = -EBUSY;
+ mutex_unlock(&cgroup_mutex);
+ mutex_unlock(&inode->i_mutex);
+ goto drop_new_super;
+ }
+ }
+ }
+
/*
* We're accessing css_set_count without locking
* css_set_lock here, but that's OK - it can only be
@@ -1111,7 +1186,8 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
if (ret == -EBUSY) {
mutex_unlock(&cgroup_mutex);
mutex_unlock(&inode->i_mutex);
- goto free_cg_links;
+ free_cg_links(&tmp_cg_links);
+ goto drop_new_super;
}

/* EBUSY should be the only error here */
@@ -1145,15 +1221,26 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
cgroup_populate_dir(root_cgrp);
mutex_unlock(&inode->i_mutex);
mutex_unlock(&cgroup_mutex);
+ } else {
+ /*
+ * We re-used an existing hierarchy - the new root (if
+ * any) is not needed
+ */
+ kfree(opts.new_root);
}

simple_set_mnt(mnt, sb);
+ kfree(opts.release_agent);
+ kfree(opts.name);
return 0;

- free_cg_links:
- free_cg_links(&tmp_cg_links);
drop_new_super:
deactivate_locked_super(sb);
+
+ out_err:
+ kfree(opts.release_agent);
+ kfree(opts.name);
+
return ret;
}

@@ -2971,6 +3058,9 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
seq_printf(m, "%lu:", root->subsys_bits);
for_each_subsys(root, ss)
seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+ if (strlen(root->name))
+ seq_printf(m, "%sname=%s", count ? "," : "",
+ root->name);
seq_putc(m, ':');
get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
cgrp = task_cgroup(tsk, subsys_id);

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